Letter to the Editor.

I read with great interest the paper by Dehvari and Ghahghaei (Dehvari and Ghahghaei, 2018 [1]). Their paper aimed to prove that biosynthesized AgNPs mediated by Pulicaria undulata L. has the capability in inhibiting amyloid fibril formation and thus could be considered as a therapeutic agent in the treatment of amyloidosis disorders. According to the literature (Jangholi et al., 2018 [2]), Thioflavin T (ThT) is a commonly used probe to monitor in vitro amyloid fibril formation. Also, since ThT fluorescence originates only from the bound population of the dye molecules, the several orders of magnitude increase in the fluorescence intensity makes ThT an unusually sensitive and efficient reporter. The authors used ThT to monitor in vitro amyloid fibril formation of α-lactalbumin and fluorescence emission spectra were recorded upon titration of the indicated concentrations of nanoparticles or α-casein. They excited the assay solutions at 450nm and the emissions were measured over the range 460-600nm. Interestingly, upon binding to α-lactalbumin's amyloid fibrils, ThT displayed a (slight) relative increase of fluorescence signal at approximately ~530-540nm, when excited at 450nm with no background ThT fluorescence subtraction/reportage. Upon binding to amyloid fibrils, ThT generally exhibits a dramatic shift of the excitation maximum (from 385nm to 450nm) and the emission maximum from 445nm to the higher wavelengths, along with a strong fluorescence signal at ~482nm (Biancalana, 1804 [3]). Regarding the wavelength of ThT fluorescence maxima, the obtained results by Dehvari and Ghahghaei are inconsistent with what has yet been reported in the literature. Moreover, the respected authors, in the present work, have not tried to describe these unusual ThT results. However, I could not find evidence/fingerprint of "cotton effect" of ThT and/or absorption flattening within the results.